An invasive European green crab was found in Washington State's inland waters for the first time.

Invasive European green crabs have been swarming up and down both coasts, but because of the flow of ocean currents around the Pacific Northwest, inland waters of BC and Washington State were thought to be relatively safe. Well, on Sept. 2, volunteers announced they'd recently caught a single crab on San Juan Island, in Puget Sound. Although it's just one for now—and it could have hitched a ride on someone's fishing gear, or another way—it's the first confirmed sighting in these inland waters.

Starting next week, a "rapid response team" will be out laying traps and trying to figure out if there are more crabs out there. The aliens pose a threat to the region's native species.

"I'll admit, I have a lot of respect for these crabs," Sean McDonald, a research scientist at the University of Washington, told me. McDonald works with the Washington Sea Grant's Crab Team, a network of citizen scientists that serves as an early alert for the crustacean's encroachment. They caught the crab, and will be organizing next week's response. "They're tough and resilient," he continued. "They make a living anywhere they can."

The Euroopean green crab was found by volunteers in Westcott Bay. Image: Craig Staude/Washington Sea Grant

European green crabs, global invaders that have been on the East Coast for a couple hundred years and appeared more recently on the Pacific coast, are notorious for destroying oysters and other shellfish, reducing invertebrate and fish diversity, and outcompeting native crabs and lobsters. They like to dig. In the Gulf of Maine, their rooting around has been disaster for eelgrass habitats that support many species of fish.

Climate change is worsening the problem, as waters become warmer and friendlier to invasive species, favouring them over many of the long-established native ones.

The West Coast crustaceans are genetically related to the ones on the Atlantic side, which means these critters must have crossed country somehow. (They were first seen in waters around San Francisco in 1989, said McDonald.) He thinks they might have hopped a lift in fishing shipments, nestled in moist seaweed packed around live lobsters.

"The lobsters would survive, but so would anything in the seaweed," he said. "Tiny green crabs like to hang out there when they're small."

The European green crab is native to the shores of the Baltic Sea and the northeastern Atlantic Ocean. Image: P. Sean McDonald/Washington Sea Grant

Canadian scientists are also taking note of the single male crab that's turned up so far, worrying they might start to appear in BC's Strait of Georgia. "We knew the horse was out of the barn on the west coast of the island," scientist Tom Therriault of Fisheries and Oceans Canada told me. European green crab larvae wash north with the currents, and can now be found as far north as central BC, he said, although Alaska remains untouched. They've been on the West side of Vancouver Island for about a decade, he said.

"This represents a fundamental shift, if it is true that they are established" in inland waters, he told me, with the big caveat that it's still just one crab so we don't know for sure.

Washington's Crab Team will be blanketing traps over the area where the critter was found, to root out as many more as they can. It's illegal to keep live European green crabs in the state, McDonald told me, so any that turn up will be euthanized.

Still, it feels like just a matter of time before more of them appear.